Change AckDeadline type to time.Duration in GCP Pub/Sub metadata

Updated the AckDeadline field in the metadata struct to use time.Duration instead of int. This change allows Dapr to interpret the acknowledgment deadline as either seconds or Go duration strings, providing greater flexibility and usability for configuring message acknowledgment timeouts.

pubsub/gcp/pubsub/pubsub.go

@@ -84,7 +84,7 @@ type WhatNow struct {
 }
 
 type metadata struct {
-    AckDeadline int `mapstructure:"ackDeadline"`
+    AckDeadline time.Duration `mapstructure:"ackDeadline"`
 }
 
 const topicCacheRefreshInterval = 5 * time.Hour